Megger DLRO 600 User Manual

M

DLRO® 600
High Current, Low Resistance Ohmmeter

USER MANUAL

GSAFETY WARNINGS

THESE SAFETY WARNINGS MUST BE READ AND UNDERSTOOD BEFORE THE INSTRUMENT IS USED.

n DLRO600 is supplied without a plug terminating the supply lead.

An appropriate plug must be fitted prior to use. The instrument can draw 25 amps when running at full current output so please ensure an appropriate plug is used.

n The DLRO200 must be grounded (earthed) when in use.

The instruments need a ground connection for two reasons.

As a safety ground.

To provide the internal voltmeter with a ground reference, so that it can alert the user if a dangerous voltage is connected to the terminals.

At switch on, an internal test circuit checks that the ground wire is connected. A single-phase supply normally has one live wire one neutral wire and a ground. The neutral is

connected to ground at some point, so that neutral and ground are both at approximately the same voltage. At switch-on there is a continuity check from ground to neutral.

(There is also a check from ground to live in case the power leads are reversed). If there is no continuity the instrument will refuse to start and the screen will remain blank.

This system works well when power is taken from a supply where there is one live phase wire and a neutral which is at ground potential. A problem arises when power is

obtained from a portable generator where the two supply wires are floating. Connecting the DLRO ground to real ground makes it safe but the internal test circuit does not
work because there is no connection between ground and the power wires.

The solution to the problem:

Connect the ground terminal to real ground (for safety).

Connect one of the power wires to ground (to enable the ground test circuit).

It is a good idea to also connect the generator chassis to ground (for safety).

n Circuits must be de-energised before testing.

The DLRO600 must only be used on dead systems. If the item under test has a voltage upon it greater than 10 volts ac peak or dc with reference to ground the DLRO600 will

indicate the presence of the voltage and prevent any tests being carried out.

n Testing inductive circuits can be hazardous:

The DLRO600 is a high power instrument, with an output power measured in kilowatts, designed for testing resistive loads. It must NOT be used to test inductive loads.

n During use the DLRO600, its current leads and the sample being tested can become hot.

This is normal and is caused by the passage of high currents. Take care when touching the instrument, current leads, clips and the test sample.

n This product is not intrinsically safe. Do not use in an explosive atmosphere.

n Ensure that the power switch is always accessible so that power can be disconnected in an emergency.

n If this equipment is used in a manner not specified by the manufacturer, the protection provided by the equipment may be impaired.

2

SYMBOLS USED IN THIS DOCUMENT AND ON THE INSTRUMENT

u Protective conductor terminal
s Hot terminals

G Refer to the User Manual for more information

1 Power On
0 Power Off

c Equipment complies with relevant EU Directives

Do not dispose of in the normal waste stream

CONTENTS

3

SAFETY WARNINGS 2

GENERAL DESCRIPTION 4

OPERATION 5

Main menu screen 5

TEST menu 6

OPTIONS menu 7

CURRENT menu 9

Warning messages 9

Entering notes in the memo screen 9

Test result storage 10

Real time downloading of test data. 10

TEST TECHNIQUES & APPLICATIONS 11

Test sequence 11

Lead resistance 11

Interference and grounding the sample 11

SPECIFICATIONS 12

Repair and Warranty 13

End of life disposal 13

The use of a four terminal measurement technique removes the test lead
resistance from the measured value although the use of lightweight current
leads may prevent the DLRO600 from producing the full requested current.
In this case the instrument will produce the highest current possible taking
into account the resistance of the current leads and the item being tested.

Before a test may be started the potential test lead contact is monitored
to ensure good contact is present. This reduces the chance of erroneous
readings and prevents arcing at the contact point, which would otherwise
damage the item under test and the test lead contacts. A resistance
measurement takes approximately 7 seconds.

DLRO600 is supplied complete with a pair of 5 metre (16 feet) current leads
terminated with large clamps, and smaller, lighter potential leads. Other
lengths and terminations are available if required.

The DLRO600 will operate with a supply voltage from 100 to 265 volts but it
will only work to full specification from 207 to 265 volts. If the input voltage
is less than 207 volts it may not be possible to obtain an output of 600 amps.
When the supply is at its lower limit of 100 volts, an output current of at least
200 amps will be possible when using the standard leads (connected to C1
and C2 terminals). If the supply voltage is low, higher output currents can be
obtained by using thicker or shorter current leads.

The large terminals C1 and C2 supply a low voltage (from zero to 5 volts)
which is adjusted automatically to produce the desired current (from 10 A to
600 A). C1 is the positive terminal. This d.c. voltage is half wave rectified and
unsmoothed, the inductance of the test leads providing sufficient smoothing
for the current.

P1 and P2 are voltage measuring terminals. P1 is nominally positive, but
connections can be reversed without affecting the measurement. All four
terminals are floating.

A warning will be given if dangerous voltages are connected to any terminal
(C or P) with respect to ground.

GENERAL DESCRIPTION

4

The Megger® DLRO® 600 is an a.c. powered low resistance ohmmeter
deigned to measure d.c. resistances in the low milliohms or microhms
using a maximum test current of 600 Amps d.c. The maximum test current
available is dependent upon the power supply, the resistance of the test
leads and the resistance of the item being tested. Full details are available
in the SPECIFICATIONS section later in this book.

The power lead entry is located on the left-hand side panel and marked
“100-265 V a.c., 25 A max., 50/60Hz”. The main On/Off switch is located
next to the power lead entry. All other controls are mounted on the front
panel. Should the supply earth be inadequate the instrument will refuse
to switch on, the display will remain blank. An additional earth terminal is
provided on the left hand side of the instrument.

Principle of operation

The required current is set before the test starts. When the TEST button
is pressed, after a short delay the current increases to the set current, the
voltage detected across the “P” leads is measured, and the current then
reduces to zero.

Operation is controlled using the two-axis paddle and the menu system,
which appears on the backlit liquid crystal display. The keyboard is used
to set the desired test current and to add notes, which may be stored with
test results in on board memory for later download via the RS232 socket
provided. The measured resistance, the actual test current and measured
voltage are clearly presented on the display after the test is complete.

After a slight pause the display will change to the Main Menu screen.

MAIN MENU SCREEN

This screen provides access to the menuing system, through which you set
up your instrument and choose the desired test parameters. Navigation of this
menuing system is by means of the cursor control and Enter key.

At the top of the screen are the three main menu choices; “TEST”,
“OPTIONS” and “CURRENT”.

Below this are details of the test current selected (SET CURRENT),
maximum current to be allowed (CURRENT LIMIT), the number of stored
tests and the current date and time.

To perform a measurement is straightforward.

1. Use the Left and Right arrows of the two-axis cursor control to
highlight the TEST menu. Use the down arrow to select the
required test type. Press Enter.

2. Use the Left and Right arrows of the two-axis cursor control to
highlight the CURRENT menu. Use the down arrow to select SET
and press Enter. Type in the desired current using the numeric keys
on the keypad. When finished press Enter.

If the current you have set is greater than the current limit, DLRO600
will beep and clear the SET CURRENT field. Re-enter the desired
current, if necessary increasing the current limit to a value equal to
or greater than the desired level. (See separate topic for setting the
current limit).

3. Connect the sample to be tested to the instrument terminals and
press the TEST button. The different test types have slightly
different connection requirements, which are detailed, in the
sections below.

OPERATION

5

Terminate the supply lead with a plug suitable for your circumstances.

Plug the instrument supply lead into a socket outlet and switch the
instrument on using the On/Off switch situated on the left side of the
instrument. The POWER lamp will illuminate, the instrument will display
the firmware version number and perform a calibration check. If this is
successful the display will show “CALIBRATED”. If the check fails the
display will show “NOT CALIBRATED”.

DLRO 600 V1.00

COPYRIGHT

MEGGER LIMITED

2002

INITIALISING HARDWARE

CALIBRATED

TEST OPTIONS CURRENT

SET CURRENT 450
CURRENT LIMIT 500

23 TESTS STORED

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